The use of tactile-readable patterns has wide application primarily at present in the use, by sight impaired or blind people, of Braille characters. These characters each comprise a particular arrangement of raised dots, which are generally imprinted out era planar paper or cardboard medium by embossment. The embossing process is both slow and expensive.
As an alternative to embossment, the use of thermography, does not appear to be successful, presumably on a basis of the high costs involved, and other possible technical problems.
In efforts to achieve lower cost, touch-readable products, many attempts have been made on the basis of silk-screen printing, without however achieving at an acceptable cost characters of sufficient prominence to enable tactile distinction thereof.
In some previous, experimental work in this field in which I participated, a flat bed silk screen was used in cooperation with an underlying stationary planar sheet upon which the ink was deposited. It was found that with this arrangement the speed of application was insufficient, leading to slumping so that a satisfactory economic result and an acceptable standard of readability could not be achieved. Also, in using the flat bed method of silk screening the maximum rate of production that could be achieved was in the range of 150 to 200 sheets per hour, which is highly uneconomical, and cost inefficient.
In case of known prior art, this includes the following patents:
PCT Norway No. 8700038, Apr. 20, 1987 PA0 PCT Netherlands No. 8200045, Dec. 15, 1982 PA0 PCT Europe No. 8800548, Jun. 22, 1988 PA0 U.S. Pat. No. 2,616,198, H. P. Sewell, Nov. 4, 1952 PA0 U.S. Pat. No. 3,372,38, K. F. Tripp, Mar. 12, 1968 PA0 U.S. Pat. No. 3,432,328, Vaurio, Mar. 11, 1969 PA0 U.S. Pat. No. 3,442,207, W. E. Johnson, May, 6, 1969 PA0 U.S. Pat. No. 3,924,19, Jacob, Dec. 2, 1975 PA0 U.S. Pat. No. 3,987,725, Scantlira Oct. 26, 1976 PA0 U.S. Pat. No. 4,571,190, Zagler et al., Feb. 18, 1986 PA0 U.S. Pat. No. 5,046,415, Oates, Sep. 10, 1991 PA0 British Patent No. 827003, Jan. 3, 1958 PA0 Japanese Patent No. 83786929,